title: Homogeneous hydrogenation and isomerization of 1-octene catalyzed by nickel(II) complexes with bidentate diarylphosphane ligands.
abstract: A systematic library of 24 nickel(II) complexes with bidentate diphosphane ligands was synthesized, and the solid-state structures of five of them were determined with X-ray crystallography. The compounds C1-C3 are common P2Ni(II)X2-type complexes, while C4 contains a unique [P2Ni(II)(NH3)(OAc)](+) square-planar structure with a P2NO donor set and C5 constitutes a rare [(P2Ni(II))2(μ-OH)2](2+) dinuclear compound. The catalytic activity of all complexes was tested in the hydrogenation and/or isomerization of 1-octene in a CH2Cl2/CH3OH reaction medium. Catalyst precursors bearing ligands with o-alkoxy aryl rings selectively hydrogentate 1-octene to n-octane, while catalytic systems comprising ligands without the o-alkoxy functionality selectively isomerize the substrate to a mixture of internal alkenes, mostly cis- and trans-2-octene. The conversion is enhanced by equipping the ligand aryl rings with electron-donating alkoxy groups, by increasing the steric bulk of the backbone and/or the aryl rings, by employing relatively noncoordinating anions, and by adding a base as the cocatalyst. Using the compound [Ni(L3X)I2] as the catalyst precursor and upon application of standard hydrogenation conditions, full conversion of the substrate was achieved in 1 h to isomerization products only (TON = 1940). When a catalytic amount of the base is added, a similar result is obtained even in the absence of H2. A maximum TON of 4500 in 1 h with 96% selectivity for n-octane was achieved by employing [Ni(oMeO-L3X)(NH3)(OAc)]PF6 as the catalyst precursor.
authors.affiliation: Gorlaeus Laboratories, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
authors.forename: Tiddo J
authors.initials: TJ
authors.lastname: Mooibroek
authors.forename: Erica C M
authors.initials: EC
authors.lastname: Wenker
authors.forename: Wietse
authors.initials: W
authors.lastname: Smit
authors.forename: Ilpo
authors.initials: I
authors.lastname: Mutikainen
authors.forename: Martin
authors.initials: M
authors.lastname: Lutz
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Bouwman
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006865:Hydrogenation; D007536:Isomerism; D008024:Ligands; D008958:Models, Molecular; D009532:Nickel / Q000737:chemistry*; D010720:Phosphines / Q000737:chemistry*
chemical_list: D000475:Alkenes; D056831:Coordination Complexes; D008024:Ligands; D010720:Phosphines; D009532:Nickel; C037690:1-octene; C044646:phosphine